As a recent development in the field of synthetic foam materials, it is known that polyurethane foam materials can be produced from suitable compositions by reacting mixtures of polyols, foam stabilizers, plasticizers and optionally additional adjuvants, such as accelerators, with an excess of organic di-isocyanates and/or higher poly-isocyanates under pressure in the presence of liquefied expanding gases to obtain prepolymers containing free isocyanate groups. This reaction is expediently carried out in a pressure vessel, e.g. in aerosol cans. Upon discharge and expansion of the composition via a pressure valve, while the expanding agent evaporates a so-called froth foam is formed, which polymerizes by action of ambient moisture on the still free isocyanate groups. These can be used in many ways, such as building materials.
Pertinent patent literature is German patent application Nos. 20 45 852, 27 58 114 and 30 22 578 as well as U.S. Pat. No. 3,830,760.
The compositions when maintained in systems under pressure have a reasonably long storage life. These are sometimes called a one component system since nothing is added to them before releasing the pressure. This is in contrast to two component systems where the organic polyol, catalyst foaming agent and additives are kept separate from the isocyanates until immediately prior to the formation of foam.
A certain disadvantage of the polyurethane foam materials thus produced is their tendency to undergo an additional volume expansion even after polymerization, rather slowly at room temperature, but relatively quickly at elevated temperature or elevated humidity of the air. Such volume expansion may lead to deformation of foam-filled objects as for example door posts or window frames.
To eliminate this disadvantage, the attempt has already been made to reduce the undesirable tendency to subsequent volume expansion to an acceptable degree by using as, a secondary expanding agent, a rather high proportion of diphenyl methane diisocyanate or by addition of trichlorofluoromethane as well as by the use of special nitrogen-containing polyols in combination with a more volatile primary expanding agent such as monochlorodifluoromethane or dichlorodifluoromethane.
However, it is still found that polyurethane foam materials of the kind here described, produced by the known methods, show, in particular, at slightly to moderately elevated temperatures of for instance 40.degree. to 70.degree. C., a subsequent volume expansion of about 10 to 15% both when stored dry and at a relative humidity of 90%.